This invention relates to apparatuses and methods for validating coins.
It is known to provide in such apparatuses one or more inductive sensors which generate electromagnetic fields in a test region through which a coin is arranged to travel. The coin influences the field to an extent dependent upon the dimensions and/or material of the coin. The inductive sensor, and the circuit to which it is coupled may be arranged so that the influence of the coin on the electromagnetic field is predominantly determined by the coin material, the coin diameter or the coin thickness.
Some coins are formed of a composite of two or more materials, and have an inner disc surrounded by an outer ring, the disc having a different metallic content from that of the outer ring. Often, each of the inner disc and the outer ring is of an homogeneous metal, but it would be possible for one or the other or both to be formed of two or more metals. For example, the inner disc may be formed of a core material with outer cladding of a different material. Coins which have an inner disc of different material content to that of a surrounding ring will be referred to herein as xe2x80x9cbicolorxe2x80x9d coins. (This expression is intended to encompass the possibility of any number of concentric rings of different materials.)
Various techniques have been developed for validating bicolor coins. One example is shown in WO-A-93/22747. The present invention is directed to a different technique which enables validation of bicolor coins using a compact validation apparatus. Other aspects are directed to validation of clad coins (formed e.g. by an outer material rolled on top of an inner material, or by plating the inner material), which may or may not be bicolor.
Various aspects of the invention are set out in the accompanying claims.
According to another aspect, the material content of the outer ring of the bicolor coin is measured using a relatively large coil wound on a ferrite whose diameter exceeds the diameter of the inner disc of each bicolor coin to be validated by the apparatus. In this way, the eddy currents generated when the coin passes the coil, and when the inner disc is within the diameter of the ferrite, are substantially confined to the outer ring of the coin, so that it is possible to take a measurement of the material content of the outer ring of the coin which is not significantly influenced either by the material content of the inner disc or by the characteristics of the interface between the disc and the outer ring.
According to certain aspects of the present invention a coil which is used to determine the material content of the outer ring of the coin is also used for determining the coin diameter. According to a still further aspect of the invention, a coil used to determine the material content of the outer ring of the coin surrounds a further coil which is used to perform a different test (e.g. a thickness test) on the coin. These aspects of the invention provide for better discrimination while maintaining a compact size of the validator.
There may be provided an additional coil for measuring the material content of the inner disc of the coin.